A conventional combination “A” of treadmill and stair climbing machine is shown in FIGS. 6, 6A, 6B and 6C, and generally includes a frame 50 with two posts 20 connected to two sides of a front end of the frame 50 and a U-shaped handle 30 is connected to the two posts 20. Two rollers 70 are connected to a rear end of the frame 50 and driven by a wheel 71 which is driven by a motor “C”. An L-shaped plate 9 is connected to the rear end of the frame 50 and supports the shafts of the two rollers 70. Two pedals 10 respectively connected to the two rollers 70 and each pedals 10 has a running belt “B” reeving the roller 70 and a front end of the pedal 10. Two hydraulic cylinders 40 are respectively connected between the two pedals 10 and two connection ports 41 on the two posts 20. Each pedal 10 has an extension 8 connected to an underside thereof and a swing mechanism 80 is connected to the two pedals 10 so that when the combination is set to be a stair climbing machine as shown in FIG. 6A, the two pedals 10 can be alternately stepped downward at the front end thereof. A T-shaped switch member 1 is connected to the front end of the frame 50 and one of two ends of its transverse bar is pivotably connected to a link 3 which is connected to a support frame 4 on which two support pieces 5 are located. Two springs 6 are respectively connected between the two support pieces 5 and the frame 50. Each extension 8 has a block 7 connected to a distal end thereof so that when operating the T-shaped switch member 1 to the position as shown in FIG. 6, the blocks 7 are supported on the support pieces 5. At this position, the two pedals 10 cannot be pivoted about the rollers 70 and are used as a treadmill.
It is noticed that the structure for transferring the treadmill and stair climbing machine, including the T-shaped switch member 1, the link 3, the support frame 4, the support pieces 5, the blocks 7, and the extensions 8, is too complicated and costly. Besides, the two pedals 10 are supported by the rollers 70 which are easily to be off-centered and this could damage the motor “C”.